Large format lenses are photographic optics that provide an image circle large enough to cover large format film or plates. Large format lenses are typically used in large format cameras and view cameras.
Photographic optics generally project a circular image behind the lens. On smaller format cameras the image circle generally covers only the intended film size with little room to spare. Large format lenses are an exception. For large format use the circular patch of image light usually extends beyond the minimum size circle needed to fully cover the rectangle of the film. The extra image offers room to spare to make use of camera movements that re-align the lens away from dead center on the film.
Lenses of the same general construction are often given a name implying this design. For example, a Tessar always has four elements in three groups as described below, although Tessars have been produced with different focal lengths and maximum apertures for many decades. Sometimes a name does not identify a specific design; Kodak's Ektar lens brand name encompasses many different types. Sometimes different manufacturers use different names for lenses of the same type; for example the Voigtländer Skopar is of Tessar design. And sometimes identical lenses are sold under different names and at different prices; for example, lenses branded as Rodenstock and Caltar.
Early lenses suffered from flare and low contrast, worsening as the number of lens-air interfaces increased. The introduction of and improvements in anti-reflective coatings vastly reduced flare; some many-element lens designs which had been abandoned due to low contrast in spite of otherwise excellent performance became practical. Lenses designed for use with monochromatic film, first orthochromatic, then panchromatic, had less exacting requirements regarding chromatic aberrations than when colour film is used. When using older lenses today one should check that chromatic aberrations and flare are acceptable for the application.
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